1. Field of the Invention
This invention relates to a vibration wave device, and particularly to the structure of a vibration member in a travelling wave type vibration wave motor.
2. Related Backgorund Art
A vibration wave motor in which a travelling vibration wave is engendered in a resilient member and a moving member such as a rotor is moved by this vibration is compact and can provide for a high torque during a low speed and therefore has been adopted for driving the photo-taking lens of a single-lens reflex camera in recent years.
FIG. 2 of the accompanying drawings is a longitudinal cross-sectional view of the photo-taking lens of a single-lens reflex camera incorporating therein a vibration wave motor for driving the photo-taking lens. The reference numeral 1 designates a circular ring-like metallic resilient member rotatable about the optic axis L of the photo-taking lens. As shown in FIG. 3 of the accompanying drawings, grooves 1A of a predetermined width t and a predetermined depth h are formed on that side of the resilient member 1 which is in contact with a rotor 3 to be described, over the entire periphery thereof. A piezo-electric element 2 such as PZT is fixed to the lower portion of the resilient member 1 by an adhesive agent. Ultrasonic driving signals of different phases are applied to the piezo-electric element 2 as an electro-mechanical energy conversion element by a conventional method, and the resilient member 1 is vibrated in response to these signals, whereby there is engendered a travelling vibration wave rotating in the circumferential direction of the resilient member 1 which forms a vibration member. The reference numeral 3 denotes a circular ring-like rotor having an end portion which is in pressure contact with the upper surface of the resilient member 1. A circular ring-like first vibration absorbing member 5 formed by rubber or like material is provided on the other end of the rotor 3 as a moving member. The reference numeral 4 designates a circular ring-like vibration insulating member formed of felt or like material. The insulating member 4 is subjected to a pressure force from two counter-sunk springs 9 superposed one upon the other with a felt bed 8 interposed therebetween.
The rotor 3 is held in close contact with a connecting plate with the aforementioned first vibration absorbing member 5 interposed therebetween. The circular ring-like connecting plate 22 is fixed to an output transmitting member 25 by six fastening screws (not shown). The output transmitting member 25 rotatable about the optic axis L constitutes a ball bearing by the use of balls 10 and ball races 13 and 14. The ball races 13 and 14 are fixed to the outer cylinder 12 of the photo-taking lens, and the outer cylinder 12 is coupled to a fixed cylinder 11 and fixed to a camera mount 19. A connecting roller 15 is fixed to the fore end of the output transmitting member 25, and is engaged with the key way (not shown) of a moving ring 17 holding a focusing lens 27 provided in the direction of the optic axis. The threaded portion 18a of a fixed inner cylinder 18 and the threaded portion 17a of the moving ring 17 are helicoid-coupled together, and by the rotational movement of the output transmitting member 25, the moving ring is movable in the direction of the optic axis while being rotated through the intermediary of the connecting roller 15.
In such a construction, a travelling vibration wave is engendered in the vibration members 1 and 2 in a conventional manner by an AF singal from the camera side or a driving signal from a manual ring 16 to thereby rotate the rotor 3 and finally move the focusing lens 27 in the direction of the optic axis, thus accomplishing focus adjustment.
In the case of such a conventional device, the vibration members 1 and 2 have been formed of a uniform material so that the travelling vibration wave for driving may be of the same amplitude and the same wavelength at any position on the vibration members, and have been of substantially uniform structure as shown in FIG. 3 of the accompanying drawings.
In the above-described conventional device, however, the error of the degree of planarity of the vibration member, the moving member or the holding member therefor has caused the irregularity of surface pressure in the surface of contact between the two (the vibration member and the moving member), and due to such a cause, a travelling vibration wave of a wavelength differing from that of the travelling vibration wave for driving has grown and thus, noise has sometimes occurred from the surface of contact between the vibration member and the moving member.
When such travelling vibration wave having a wavelength causing the production of noise has been analyzed, it has been found that in one case, this travelling vibration wave is of a single wavelength and in another case, it is of a plurality of wavelengths.